add stefanprobst as a contributor for code, and test (#201)

* update README.md

* update .all-contributorsrc

Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>

Author: allcontributors[bot]

.all-contributorsrc

@@ -220,6 +220,16 @@
       "contributions": [
         "doc"
       ]
+    },
+    {
+      "login": "stefanprobst",
+      "name": "stefanprobst",
+      "avatar_url": "https://avatars.githubusercontent.com/u/20753323?v=4",
+      "profile": "https://github.com/stefanprobst",
+      "contributions": [
+        "code",
+        "test"
+      ]
     }
   ],
   "commitConvention": "none"

README.md

@@ -839,6 +839,7 @@ Thanks goes to these people ([emoji key][emojis]):
     </tr>
     <tr>
       <td align="center"><a href="https://github.com/theMosaad"><img src="https://avatars.githubusercontent.com/u/48773133?v=4?s=100" width="100px;" alt="Mosaad"/><br /><sub><b>Mosaad</b></sub></a><br /><a href="https://github.com/kentcdodds/mdx-bundler/commits?author=theMosaad" title="Documentation">📖</a></td>
+      <td align="center"><a href="https://github.com/stefanprobst"><img src="https://avatars.githubusercontent.com/u/20753323?v=4?s=100" width="100px;" alt="stefanprobst"/><br /><sub><b>stefanprobst</b></sub></a><br /><a href="https://github.com/kentcdodds/mdx-bundler/commits?author=stefanprobst" title="Code">💻</a> <a href="https://github.com/kentcdodds/mdx-bundler/commits?author=stefanprobst" title="Tests">⚠️</a></td>
     </tr>
   </tbody>
 </table>